Pick-and-place equipment is commonly used to assemble integrated and discrete components onto printed circuit boards (PCBs). Various models and manufacturers of pick-and-place equipment exist, for example a Model IP-II available from Fuji America Corporation of Lincolnshire, Ill., among others. The pick-and-place equipment removes the component from a first position, for example from a tape-and-reel, aligns the component with the PCB, and places it into its proper location on the PCB. Solder on the PCB is heated to electrically connect the component into its proper location on the PCB.
To ensure the proper alignment of the component on the PCB, the pick-and-place equipment must be calibrated. This calibration is typically achieved with actual electronic components and printed circuit boards. The components are assembled onto the PCB by the pick-and-place equipment, then the alignment of the devices is checked using visual inspection with an unaided eye or using a microscope. If the devices are determined by a technician to be misaligned in the X-, Y-, or Theta (rotational) axes, adjustments to the pick-and-place equipment are performed. The process continues until an acceptable alignment of the component to the PCB is established. A similar calibration system is described in U.S. Pat. No. 4,776,088 which is incorporated herein by reference.
Various problems are associated with present methods of calibrating pick-and-place equipment. For example, the components and PCBs themselves are allowed certain manufacturing tolerances, which thereby make their use as a calibration tool questionable. A component that is at the outer range of a design tolerance, if used to calibrate the equipment, may provide for a less than ideal target for the majority of devices which adhere more closely to the design goal. Also, the alignment which is considered acceptable can vary from one technician to another even with training, as there is no quantitative measurement typically employed to pass or fail the alignment of a device to the PCB. As a result of the lack of quantitative measurements there is no means to statistically assess the machine's repeatability and capability.
A method and apparatus which allows for an accurate, quantitative, repeatable calibration of pick-and-place equipment would be desirable.